By using a liquid rapid solidification method, various amorphous, fine crystalline, and polycrystalline alloy-based materials have been developed. Functional materials, such as a shape-memory alloy, in the form of a thin belt, a thin wire, and a powder can be formed by a liquid rapid solidification method (Patent Documents 1 and 2).
As for an iron-based magnetic shape-memory alloy, one (Furuya) of the inventors of the present invention found a giant magnetostrictive effect by using a liquid rapid solidification method which is equivalent to the level of Terfenol-D known as a giant magnetostrictive material. This new magnetostrictive material is a practical polycrystalline material having a particular crystal controlled texture which is fine and has strong directionality peculiar to a rapidly solidified material, and a patent application relating to a polycrystalline Fe—Pd-based and a Fe—Pt-based alloy was filed (Patent Document 3). In addition, the inventors of the present invention reported properties of a thin belt-shaped sample of a Fe-15 at % Ga alloy which was annealed for a short period of time (1,173K for 0.5 hour) (Non-Patent Document 1).
Furthermore, it was also found that when a NiCoGa, a CoNiGa-based alloy (Patent Document 4) and a Fe—Ga-based alloy (Patent Document 5) are processed at a certain rapid cooling rate, a fine columnar crystal texture having significantly strong crystalline anisotropy can be formed, and that the material thus controlled also has ductility and can induce a magnetostrictive phenomenon 6 to 10 times or more that of a conventional randomly oriented crystalline material.
However, an alloy having high performances as described above has been realized primarily by a thin belt or a thin wire having a thickness or a diameter of approximately 200 μm or less, and it has been difficult to obtain a material having predetermined properties by a melt method. Heretofore, as a method for producing a bulk crystalline alloy in the form of a plate, a bar, or the like having a thickness or a diameter in the order of millimeters or more, besides a melt method, a powder metallurgical method has been known. As one powder metallurgical method, a spark plasma sintering method has been known (for example, see Non-Patent Document 2 and Patent Document 6).
In the spark plasma sintering method, high energy pulses can be concentrated on positions at which intergranular bonds are intended to be formed, and hence a sintering process dynamically proceeds. This is the feature of the spark plasma sintering process and is significantly different from a general quasi-static sintering method such as hot pressing or resistance sintering. Since rapid temperature increase only on grain surfaces can be performed by self-heating, while the grain growth of a sintering raw material is suppressed, a dense sintered body can be obtained within a short period of time. In addition, since the texture inside the sintering raw material can be prevented from being changed, a powdered material having an amorphous structure or a nanocrystalline texture can be formed into a bulk shape such as a plate or a bar while maintaining its own structure or texture. By using this electrical spark plasma sintering method, a Fe—Dy—Tb-based or a rare earth element-transition metal-based giant magnetostrictive material formed into a desired shape has been developed (Patent Documents 7, 8, and 9).    Patent Document 1: Japanese Unexamined Patent Application Publication No. 1-212728 (Japanese Patent No. 2589125)    Patent Document 2: Japanese Unexamined Patent Application Publication No. 6-172886    Patent Document 3: Japanese Unexamined Patent Application Publication No. 11-269611    Patent Document 4: Japanese Unexamined Patent Application Publication No. 2003-96529    Patent Document 5: Japanese Unexamined Patent Application Publication No. 2003-286550    Patent Document 6: Japanese Unexamined Patent Application Publication No. 7-216409 (Japanese Patent No. 2762225)    Patent Document 7: Japanese Unexamined Patent Application Publication No. 5-105992    Patent Document 8: Japanese Unexamined Patent Application Publication No. 11-189853    Patent Document 9: Japanese Unexamined Patent Application Publication No. 2001-358377    Non-Patent Document 1: authored by C. Saito, Y. Furuya, T. Okazaki, T. Watanabe, T. Matsuzaki, and M. Wuttig, Mater. Trans., JIM, vol. 45, pp. 193 to 198, Feb. (2004).    Non-Patent Document 2: authored by M. Omori, Mater. Sci. Eng. A, vol. 287, pp. 183 to 188, Aug. (2000).